Solaren - discussions, analysis, patents, timescale, etc.

Rand Simberg doesn't see how Solaren can make the numbers add up to a viable space based solar power system: How Do The Numbers Work? - Transterrestrial Musings. See also a discussion here.

I earlier mentioned a patent by Spirnak. Here is a one that is specific to SBSP: Space-based power system, James E. Rogers, Gary T. Spirnak, Patent number: 6936760, August 30, 2005.

As with the previous patent, the key technology in the SBSP patent involves a control system for keeping free-floating elements in careful alignment without the need for a supporting structure, thereby eliminating that mass. The patent says that a plurality of the

power system elements are free-floating, and the plurality of power system elements are arranged to collect sunlight, generate electrical energy from the collected sunlight, and convert the electrical energy into a form for transmission to a pre-determined location, and

the distributed control system maintains alignment of the one or more free-floating power system elements based on communications between control system components of adjacent power system elements.

Other claims in the patent describe elements with a foldable spherical mirror with "a diameter of about 1 km to about 2 km" and "supported by an inflatable tube".

I'm still reading through it, (see the patent description) but the key concepts in the patent thus involve building the SBSP power plant out of a collection of separate, free floating power generating elements, each with its own lightweight mirror, power conversion and transmission systems, etc.

Regarding the overall project, here are some miscellaneous details gleaned from the articles:
/-- PG&E has seen the design but "buried all the technical and economic details of the proposal in the confidential section of its regulatory filing" - WSJ
/-- PG&E takes the proposal seriously after seeing the details: "'We're convinced it's a very serious possibility that they can make this work,'" said PG&E spokesman Jonathan Marshall." - SFGate.
/-- Solaren claims that the 200MW, geostationary system can be launched on four vehicles that can put 25tons in LEO per launch: "Boerman [Solaren's director of energy services] said the solar installation would require four rocket launches. It would not, however, require assembly by astronauts, instead unfolding on its own in space." - SFGate.
/-- How the system gets from LEO to GEO and how much mass gets there haven't been revealed.
/-- This seems like something you would decide on early in the system design: "Solaren still hasn't decided whether to use crystalline silicon solar cells or newer, thin-film cells that weigh less than silicon but aren't as efficient." - SFGate. (I'll note that rad hardness of newer high efficiency thin-film cells could be an issue.)
/-- Solaren currently has about 10 employees and they come with Hughes Aircraft Company and US Air Force experience.
/-- Before it launches the operational system in 2016, Solaren will have tested and evaluated "critical SSP system deployments and functionality in space". - Next100
/-- "More details on Solaren�s pilot plant are expected this summer" according to Spirnak - WSJ

Posted 04/14/09 | 19:08:39 by TopSpacer | Filed under: Space Technology

Comments

I don't have time to study the patent, but based on your description of it it sounds like they need to go back and look at prior art from Ivan Bekey and others from the mid-1970s. Such approaches have been proposed before. while they will reduce mass somewhat, this not a breakthrough.

We need to get to a few hundred dollars a pound to GEO for this to be taken seriously.

Posted by Gary C Hudson at 04/14/09 20:05:00

To me the big question is whether they (or their competitors, there's that other space based solar power company recently mentioned as well) have any tricks up their sleeve when it comes to greatly increased transmission efficiency. That's the main and perhaps impossible challenge of SBSP: solve that and everything else becomes "easy".

Posted by Habitat Hermit at 04/15/09 21:14:11

Hi Gary,
There's been a lot of work over the years in development of formation satellite flying. Perhaps these guys were involved in that. Their particular implementation of the concept of control and alignment of free-flying spacecraft may differ from Bekey's.

Hi HH,
Why do you think transmission efficiency is too low? The Goldstone proof of principle test in 1975 achieved 82.5% for 34kW transmission. A lot of development in microwave technology has gone on since then. Yes, the distance to GEO is a lot farther but there don't seem to be any fundamental reasons that similar efficiencies can't be achieved if the transmitter and rectenna are sized appropriately.

http://en.wikipedia.org/wik...

http://video.google.com/vid...

- C.

Posted by TopSpacer at 04/15/09 22:40:18

Clark, the issue with formation flying is you have to be able to keep station. That either requires propellant expenditure, physical connection with tension or compression members that can handle loads and torques, or use of force fields (magnetic or electrostatic or something else we haven't invented as yet...). Most formation flying in LEO proposals use either conventional propulsive control or something exotic like magnetic fields which may work in principle but are a long way from translation into practice in orbit. I'll be very interested in seeing more on what they propose.

Posted by Gary C Hudson at 04/16/09 09:12:09

Because "sized appropriately" for the current transmission efficiencies is a severely limiting factor one way or the other. It would probably have been more intelligible of me to word it in such a way with focus upon size but that's not the perspective I view the problem from since I consider the size a secondary effect of the efficiency problem rather than the other way around ^_^

Due to the problem of transmission efficiency the minimum size of the antenna (a very big minimum size) is the primary constraint on possible implementations of SBSP and sets a minimum for overall size and thus also the effort and money needed, what it can be used for and how: it dominates every aspect of it and even when the physics of it work out acceptably it's probably still the part that needs a solution for the economics of it all to work out as well.

No matter which way one might choose to view the problem your Wikipedia link confirms it:
/"Power beaming by microwaves has the difficulty that for most space applications the required aperture sizes are very large. For example, the 1978 NASA Study of solar power satellites required a 1-km diameter transmitting antenna, and a 10 km diameter receiving rectenna, for a microwave beam at 2.45 GHz. These sizes can be somewhat decreased by using shorter wavelengths, although short wavelengths may have difficulties with atmospheric absorption and beam blockage by rain or water droplets. Because of the Thinned array curse, it is not possible to make a narrower beam by combining the beams of several smaller satellites."/

Posted by Habitat Hermit at 04/16/09 09:45:07

Hi Gary,
Yes, the patent talks some about how to maintain the position of the elements. E.g. on page 23 of the Description pdf it says,

"In an alternative embodiment, the proximity control system 13 uses a solar wind, primarily, and ion thrusters and electrostatic forces secondarily, to maintain the correct positions and orientations of the power system elements. The reflectors and fold mirrors can have paddle-like structures mounted on their circumference....By the proper rotation of the paddles, torques and forces can be imparted to the reflectors and fold mirrors."

Goes on later to say,

"...in another embodiment, the proximity control system uses orbits, for example, about the Earth or other celestial body, so that the consumption of station-keeping fuel by the heaviest system elements is minimized. The other elements (e.g. fold mirrors of an optical or RF system) are positioned to maintain focus, alignment, boresight, etc. Since the latter elements are lighter, the station-keeping fuel required by the entire system is reduced."

They also mention that for elements that are close together, they could use electrostatic forces with light tethers to keep them fixed distance apart.

- Clark

Posted by TopSpacer at 04/16/09 10:19:09

Hi HH,
Yes, it's a big area but some dual use appears feasible. The rectenna would be quite transparent to sunlight and would allow the land below it to be used for farming and pastures. The intensity of the beam is already low and the rectanna absorbs almost all of it so the farmers and cows would be safe!

5.8GHz is also being considered. The rectenna in that case could be onsiderably smller than that for 2.48GHz. See, e.g.
http://www.sspi.gatech.edu/...

- Clark

Posted by TopSpacer at 04/16/09 11:00:15

I'm not worried about the various rectenna sizes. They're not the kind of showstopper that the antennas are, or at least have been so far. A 10 km rectenna on Earth is a trivial problem compared to a 1 km diameter antenna in space (or even a 500 m diameter antenna).

Posted by Habitat Hermit at 04/16/09 12:48:37

And I should add that I know about antenna designs that can be printed on foil. Let's suppose one can use that approach: 3.1415 square km of (possibly rotating) foil does not make things significantly easier ^_^

Posted by Habitat Hermit at 04/16/09 13:11:21

Hi HH,
Well, for argument's sake, I'm giving the Solaren folk the benefit of the doubt at the moment that they know how to build big lightweight inflatable structures. They also need those for the concentrator after all. We'll see eventually if they really do in fact have practical ways of doing this.
- Clark

Posted by TopSpacer at 04/16/09 16:57:48

The most interesting patent Solaren has is for turning hurricanes with a sunsat. If the property damage done by Katrina could have been averted, how many hundreds of billions of dollars would the US government have saved?

Could transport from LEO to GEO of an automatically deployed inflatable 200 MW sunsat be accomplished by electromagnetic towing tethers, powered by the sunsat itself? I think it is technically feasible, and if anyone has any experience with that it would Hughes Engineers building sats for USAF.

Pete Worden and Elon Musk know a great deal about the real capability of existing expendable rockets, however let me point out that Musk has publically admitted that everything he "knew" about the economics of rockets changed over the time period of the development of his Falcon 1.

Pete Warden may be correct about the need to reduce the cost of space transport to GEO by a factor of 1000 to make a Sunsats econmical when compared to earth based coal fired power plants. However recent developments in materials science, specifically Colossal Carbon Tube technology by Prof. Y. T. Zhu at North Carolina State University, coupled with the recent advances by Prof. Windle's materials science team at Cambridge, where they are making macroscopic carbon yarn 18 miles long
may make it possible to build a stationary space elevator today, in which case, all bets against the economics of sunsats are off.

http://en.wikipedia.org/wik...

Posted by Tony Rusi at 04/22/09 08:41:15

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